that room you speak of must be accessed via another direction. Namely the east and west corridor entrances. You can't change the pathway from the north and south entrances. So give up on that section for now, it'll only cause unneeded headache. One easy key to acquire is from the entrance. Walk through two walls to the right (yes walk through!) to get one key. Another is, if you go up and I 'think' left a few screens to find some stairs leading down, you will need to go right one screen and walk north through two more walls to get to an area where you can get a second key.

Hope this helps. Level 6 is really confusing, I can guarantee that!

Also Patrick, if it helps, try going to the Ice Palace early and brave the invisible enemies and get the golden arrow. Makes those Gohmas much easier. If not, simply skip level 6 for now and come back later after level 7. It seems you got enough items already to find levels 7 and 8. So level 6 can wait. :)